The present invention relates generally to bar code scanners and more particularly, to a bar code scanner housing assembly which seals the bar code scanner from spilled liquids and other contaminants to which such scanners may be exposed in normal use in a point of sale environment such as a supermarket. The present invention also relates to a bar code scanner housing assembly which permits convenient replacement of components exposed to such spilled liquids and contaminants.
Supermarket checkout counters commonly include optical scanners mounted therein for optically scanning bar code labels on products to be purchased as the products are moved over scanning windows comprising at least a portion of the top surfaces of such scanners. These optical scanners, referred to herein as bar code scanners, typically include a housing or enclosure which contains a source of laser light, scanning optics for directing a scanning beam to sweep across a surface to be scanned in one or more scan lines, a lower sealed window through which the scanning beam and returning light may be transmitted, and a cartridge or cassette having another window, referred to as the upper window. The cartridge is removable and field replaceable upon being scratched or broken.
In order for the bar code scanner to operate in an optimal fashion, both the upper and lower windows must be optically transparent and free of scratches, smears, discolorations and other contaminants which would prevent the scanning beam and returning light from passing unimpeded through the windows. The upper window mounted in the cartridge is the most susceptible to such damage since it is subjected to abrasion caused by products as they move across the supermarket checkout counter. Accordingly, it has been necessary to replace the upper window more often than desired. Since prior art bar code scanner assemblies have included an upper window that is permanently affixed within a cartridge, the entire cartridge has typically been replaced in order to replace the upper window, thus increasing the expense of maintaining such a bar code scanner. Therefore, it would be desirable to have a bar code scanner having a housing assembly which permits the window to be replaced without replacing an entire cartridge.
The upper surfaces of window cartridges used in prior art bar code scanners are typically not entirely flush or smooth as a result of having the upper window mounted within the cartridge. Ridges and/or indentations are formed around the upper window at the surface of the window cartridge. Consequently, a product to be scanned must be lifted, tilted or twisted so as to slide the product across the surface of the upper window through which the scanning beam is transmitted to read a bar code label. The upper window is subjected to abrasion caused by such twisting, tilting and/or lifting of the products in addition to the abrasion caused by sliding the products over the window surface. Moreover, the throughput time for the products is increased which is undesirable. Of more concern are the significant number of checkout clerks that develop "carpal tunnel" syndrome from the systematic and continuous twisting, turning and lifting of products over the ridges and indentations found on the window cartridge surface of prior art bar code scanners. Accordingly, it is desirable to have a housing assembly for a bar code scanner which includes a cartridge having a surface that is substantially flush or smooth.
Typical bar code scanner housing assemblies include a space or gap between the lower window and the upper window which must be tightly sealed so as to preclude liquids and dust from seeping through to the lower window. When such contaminants seep through the window cartridge, the lower window must be cleaned. This is frequently difficult and time consuming, and decreases bar code scanner availability. After a significant amount of contaminants seep onto the lower window, it must be replaced. Replacement of the lower window significantly adds to the maintenance costs for a bar code scanner. Moreover, the lower window is not easily replaced since it is not contained, for example, in a removable cartridge. Rather, the lower window is typically permanently mounted in the housing. Previous bar code scanners have not included housing assemblies which seal the space defined between the upper window and the lower window. The effective sealing of this space is necessary to prevent contaminants from seeping onto the lower window. The size of the space between the windows varies significantly since the windows may have a multitude of sizes and shapes. It would therefore be desirable to have a bar code scanner housing assembly which seals the space between the upper and lower windows such that contaminants are precluded from seeping through to the lower window.
A common feature found in most bar code scanners is a mask on the upper window which minimizes the amount of ambient light passing through the window into the housing. Most environments in which bar code scanners operate are highly lighted. This has the potential of subjecting the optical components enclosed in the housing to a significant amount of ambient light. If too great an amount of ambient light were permitted to enter the housing, the signal-to-noise ratio would be reduced, preventing the bar code scanner from operating in an optimal fashion. The mask limiting the level of ambient light is typically formed from a polymeric material and disposed on the upper window in a variety of patterns. A common technique is to form the mask directly on the upper window via a silk screening technique. However, the silk screening technique is relatively expensive. Additionally, the mask must be replaced as often as the upper window since it is permanently formed on the upper window. Thus, it is desirable to have a bar code scanner which includes a mask for minimizing the amount of ambient light absorbed by the bar code scanner which requires replacement less frequently and is less expensive than those used in the past.
Accordingly, there is a need for a bar code scanner housing assembly which permits the convenient and less expensive replacement of worn components and which prevents spilled liquids and other contaminants from seeping onto the lower window of the housing assembly. There is also a need for a bar code scanner housing assembly which reduces wear of the upper components of the housing assembly and which reduces the amount of ambient light collected by the optical components of the housing assembly.